Radiation curable optical fiber coating composition

ABSTRACT

Provided is a radiation-curable, glass optical fiber coating composition which when suitably cured exhibits resistance to attack from hydrocarbon gel cable filing material. The composition contains 
     about 10 to about 90% by weight of a first radiation-curable oligomer; 
     from 0 to about 40% by weight of a reactive diluent; 
     from 0 to about 40% by weight of a photoinitiator; 
     from 0 to about 10% by weight of a pigment; and 
     about 10 to about 90% by weight of a second radiation-curable oligomer according to the following formula: 
     
         R.sup.1 -L.sup.1 -C.sup.1 -L.sup.2 -R.sup.2                (1) 
    
     where: 
     R 1  and R 2 , independently, each represent a radiation-curable functional group; 
     L 1  and L 2 , independently, each represent an alkyleneoxy chain having from about 2 to about 40 carbon atoms, wherein L 1  and L 2  are linked to C 1  through an oxygen atom 
     C 1  comprises a hydrocarbon having from about 5 to about 40 carbon atoms and containing at least one cyclic group.

This is a division of Application Ser. No. 08/615,857, filed Mar. 12,1996, now U.S. Pat. No. 5,837,750, which is a CIP of Application Ser.No. 08/403,521, filed Mar. 13, 1995 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a radiation curable optical fiber coatingcomposition which after curing results in a coating having enhancedresistance to moisture and hydrocarbon gel. The invention furtherrelates to a pigmented radiation curable coating composition suitablefor use as an outer primary coating for optical fibers.

2. Description of Related Art

Optical fibers are frequently coated with two superposed radiationcurable coatings, which together form a primary coating. The coatingwhich contacts the glass is called the inner primary coating and theoverlaying coating is called the outer primary coating. In olderreferences, the inner primary coating was called the primary coating andouter primary coating was called the secondary coating, but for reasonsof clarity, that terminology was abandoned by the industry in recentyears.

The inner primary coating is usually a soft coating providing resistanceto microbending. Microbending can lead to attenuation of the signaltransmission capability of the coated fiber and is thereforeundesirable. The outer primary coating, which is exposed, is typically aharder coating providing desired resistance to handling forces, such asthose encountered when the fiber is cabled.

The coating compositions for the inner and outer primary coatinggenerally comprise a polyethylenically unsaturated oligomer in a liquidethylenically unsaturated medium.

Usually the optical fibers are glass fibers.

Optical glass fibers are weakened upon exposure to water. For example,moisture in air can cause weakening and the eventual breakage of glassfibers. It is therefore desirable that the inner and outer primarycoating prevent moisture from attacking the glass substrate. However,many conventional coating compositions have a peak water absorptiongreater than 1.7% and therefore are not effective in protecting theglass substrate from moisture.

In addition to causing the weakening of glass substrates, moisture canalso cause the coating layers to delaminate from each other and/or theglass surface. The delamination of the inner primary coating can resultin a weakened glass substrate, because the inner primary coating can nolonger protect the glass from attack from moisture.

To avoid moisture damage to the glass surface, it is desirable toprovide a coating composition having low water absorption, resistance todelamination from glass, and a low water soak extraction. Moreover acoating composition for optical glass fibers preferably should alsoprovide a cured coating having sufficient adhesion to the glass fiberand yet be strippable for field applications.

For certain applications, conventional coating compositions do notprovide cured outer primary coatings having the required combination ofsufficient adhesion to the inner primary coating, strippability,resistance to water absorption, and a low water soak extraction.

Furthermore, it is frequently desired to color an outer primary coatingto facilitate the selection of the optical fiber which is desired fromamong many glass fibers in a cable assembly. Published European PatentApplication No. 418829 discloses the use of radiation curable ink or acolored solvent borne lacquer to color or overcoat an optical fiberwhich has already been coated with an inner and outer primary coating.This requires a third coating operation which is undesirable.

It has been proposed to include sufficient pigment for desiredcoloration directly into the outer primary coating. Such a pigmentedouter primary coating is disclosed in published PCT application WO90/13579, which describes an outer primary coating compositioncontaining pigment particles having a size of less than about 1 micron.

Published Japanese patent application No. 64-22975 describes an inkcomposition comprising a UV-curable resin and a ethoxylatedbisphenol-A-diacrylate. This reference does not disclose using thecomposition as an outer primary coating nor how to improve the moistureresistance of an outer primary coating. Moreover, the compositiondisclosed in JP-A-64-22975 is not suitable as an outer primary coatingbecause, when cured, the coating does not have the required toughness toprotect the optical glass fiber during handling.

Conventional pigmented outer primary coating compositions, when cured,have insufficient resistance to moisture. When the conventional curedpigmented coating is exposed to water, dimensional changes occur. Thesedimensional changes can lead to attenuation of the signal transmissioncapability of the glass optical fiber. Therefore, there is still a needfor a coating composition suitable for use as an outer primary coating,which can be pigmented, and which provides a cured coating having lowwater absorption, a low water soak extraction, and resistance to attackfrom hydrocarbon gel cable filling material.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a coating compositionsuitable for use as an outer primary coating which can be pigmented.Another object of the invention is to provide an outer primary coatingcomposition that when cured exhibits a low water absorption, a low watersoak extraction, and resistance to attack from hydrocarbon gel cablefilling material.

The above object and other objects are obtained by providing aradiation-curable, glass optical fiber coating composition which, whensuitably cured, exhibits resistance to attack from hydrocarbon gel cablefiling material. The uncured composition comprises:

A. about 10 to about 90% by weight of a radiation-curable oligomer;

C. from 0 to about 40% by weight of a reactive diluent;

D. from 0 to about 40% by weight of a photoinitiator;

E. from 0 to about 10% by weight of a pigment; and

B. about 10 to about 90% by weight of a second radiation-curableoligomer according to the following formula:

    R.sup.1 -L.sup.1 -C.sup.1 -L.sup.2 -R.sup.2                (1)

where:

R¹ and R², independently, each represent a radiation-curable functionalgroup;

L¹ and L², independently, each represent an alkyloxy chain having fromabout 2 to about 40 carbon atoms, wherein L¹ and L² are linked to C¹through an oxygen atom;

C¹ comprises a hydrocarbon having from about 5 to about 40 carbon atomsand containing at least one cyclic group.

The weight percentages are relative to the total weight of components A.through E.

The composition, when cured, results in coatings having improved waterresistance. When exposed to moisture, the coated glass optical fiberswells less than conventional fibers, providing enhanced concentricityof the coated glass optical fibers. Enhanced concentricity of coatedoptical fibers results in greater tolerances in the production processand increased yields. Furthermore, swelling of the coating can causeundesired microbending of glass optical fiber.

This invention also relates to an optical glass fiber coated with aninner primary coating and the above outer primary coating. The outerprimary coatings according to the invention exhibit good colorpermanence.

This invention also provides a coated glass optical fiber coated with acoating having a room temperature tensile modulus of at least about 50MPa, an elongation at break of at least about 3%, a glass transitiontemperature Tg (tan delta max) of at least about 25° C., and a peakwater absorption of no more than 1.7. The coating comprises a suitablyradiation-cured, glass optical fiber coating composition. The coatingcomposition in uncured form comprises a radiation-curable coatingcomposition comprising a radiation-curable oligomer according to thefollowing formula:

    R.sup.1 -L.sup.1 -C.sup.1 -L.sup.2 -R.sup.2                (1)

where:

R¹ and R², independently, each represent a radiation-curable functionalgroup;

L¹ and L², independently, each represent an alkyloxy chain having fromabout 2 to about 40 carbon atoms, wherein L¹ and L² are linked to C¹through an oxygen atom;

C¹ comprises a hydrocarbon having from about 5 to about 40 carbon atomsand containing at least one cyclic group.

DETAILED DESCRIPTION OF THE INVENTION

The cured outer primary coating, made by curing the above coatingcomposition, has a room temperature tensile modulus of at least about 50MPa, an elongation at break of at least about 3%, a Tg (tan delta max)of at least about 25° C., and a peak water absorption of no more than1.7, as defined herein. Preferably, an outer primary coating, made bycuring the coating composition, has a room temperature tensile modulusof at least about 400 MPa, an elongation at break of at least about 5%,a Tg of at least about 40° C., and a peak water absorption of no morethan about 1.5. The outer primary coatings according to the inventionhave a good color permanence.

The radiation-curable oligomer A. can be any radiation-curable oligomerused in radiation-curable, glass optical fiber coating compositions. Oneskilled in the art knows how to select and use radiation-curableoligomers in order to achieve the desired properties. An example of asuitable radiation-curable oligomer A. includes an urethane oligomerhaving a molecular weight of at least about 500 and containing at leastone ethylenically unsaturated group that can be polymerized throughactinic radiation. Preferably, the oligomer A. has two terminalradiation-curable functional groups, one at each end of the oligomer.

Preferably, the molecular weight of the oligomer A. is at least about700 and at most about 10,000 Daltons. More preferably the molecularweight is between about 1000 and about 5000, and most preferably,between about 2000 and 4000 Daltons. Molecular weight, as usedthroughout this application, is the calculated molecular weight of themolecule concerned. In the case of a polymer structure, it is thecalculated average molecular weight of the expected structure based onthe starting materials and the reaction conditions. The molecular weightcan also be determined using conventional techniques.

Preferably, the oligomer A. is substantially free of isocyanatefunctionality.

The radiation-curable oligomer A. is preferably present in an amount ofabout 20 to about 40% by weight, and more preferably about 25 to about35% by weight. All weight percentages used herein are expressed aspercentages relative to the total weight of components A. through E.present in the composition.

Examples of suitable radiation-curable functional groups which can bepresent on the oligomer A. include ethylenically unsaturated groupshaving (meth)acrylate, vinylether, acrylamide, maleate or fumaratefunctionality. The language "(meth)acrylate" as used herein, meansmethacrylate, acrylate, or mixtures thereof.

Preferably, the radiation-curable group in the oligomer A. is an(meth)acrylate or vinylether group. Most preferably, theradiation-curable group is an acrylate group.

Another type of radiation-curable functionality generally used isprovided by, for example, epoxy groups, or thiol-ene or amine-enesystems. Epoxy groups can be polymerized through cationicpolymerization, whereas the thiol-ene and amine-ene systems are usuallypolymerized through radical polymerization. The epoxy groups can be, forexample, homopolymerized. In the thiol-ene and amine-ene systems, forexample, polymerization can occur between a group containing allylicunsaturation and a group containing a tertiary amine or thiol.

Preferably, the oligomer A. contains at least two ethylenicallyunsaturated groups which are bound to an oligomer backbone. For example,ethylenically unsaturated groups can be present at each end of theoligomer backbone as reactive termini. The oligomer backbone can have amolecular weight of at least about 200, and can be, for example, basedon a polyether, polyolefin, polyester, polycarbonate, or copolymersthereof. Preferably, the oligomer backbone is a polyether. The molecularweight of the oligomer backbone is preferably at least about 250, morepreferably at least about 400, and most preferably at least about 600.The molecular weight is preferably not more than about 10,000, morepreferably not more than about 5,000, and most preferably not more thanabout 3000.

The oligomer backbone can comprise one or more polymer blocks coupledwith each other via, for example, urethane linkages.

Preferably, the backbone-oligomer is a polyether, a polyolefin, apolyester, a polycarbonate, or copolymers thereof. If the oligomerbackbone is a polyether, the resulting coatings have a low glasstransition temperature and good mechanical properties. If the oligomerbackbone is a polyolefin, the resulting coatings have a further improvedwater resistance.

Oligomer A. can be, for example, prepared by reaction of (i) an oligomerpolyol, (ii) a diisocyanate and (iii) a hydroxy functional ethylenicallyunsaturated monomer, for example hydroxyalkyl(meth)acrylate.

If a oligomer backbone polyol is used, preferably it has on average atleast about 2 hydroxyl groups. The oligomer backbone polyol may have, onaverage, more than 2 hydroxyl groups. Examples of such an oligomer diolinclude polyether diols, polyolefin diols, polyester diols,polycarbonate diols, and mixtures thereof. Polyether and polyolefindiols, or combinations thereof, are preferred.

If a polyether diol is used, preferably the polyether is a substantiallynon-crystalline polyether. Preferably, the polyether comprises repeatingunits of one or more of the following monomer groups: ##STR1##

Hence, the polyether can be made from epoxy-ethane, epoxy-propane,tetrahydrofuran, methyl-substituted tetrahydrofuran, epoxybutane, andthe like.

An example of a polyether polyol that can be used is the polymerizationproduct of 20 percent by weight of 3-methyltetrahydrofuran and 80percent by weight of tetrahydrofuran, both of which have undergone aring opening polymerization. This polyether copolymer contains bothbranched and non-branched oxyalkylene repeating units and is marketed asPTG-L 1000 (Hodogaya Chemical Company of Japan). Another example of apolyether that can be used is PTG-L 2000 (Hodogaya Chemical Company).

If a polyolefin diol is used, the polyolefin is preferably a linear orbranched hydrocarbon containing a plurality of hydroxyl end groups.Preferably, the hydrocarbon is a non-aromatic compound containing amajority of methylene groups (--CH₂ --) and which can contain internalunsaturation and/or pendent unsaturation. Fully saturated, for example,hydrogenated hydrocarbons, are preferred because the long term stabilityof the cured optical fiber coating increases as the degree ofunsaturation decreases. Examples of hydrocarbon diols include, forexample, hydroxyl-terminated, fully or partially hydrogenated1,2-polybutadiene; 1,4-1,2-polybutadiene copolymers,1,2-polybutadiene-ethylene or -propylene copolymers, polyisobutylenepolyol; mixtures thereof, and the like. Preferably, the hydrocarbon diolis a substantially, fully hydrogenated 1,2-polybutadiene or1,2-polybutadiene-ethene copolymer.

Examples of polycarbonate diols are those conventionally produced by thealcoholysis of diethylene carbonate with a diol. The diol can be, forexample, an alkylene diol having about 2 to about 12 carbon atoms, suchas, 1,4-butane diol, 1,6-hexane diol, 1,12-dodecane diol, and the like.Mixtures of these diols can also be utilized. The polycarbonate diol cancontain ether linkages in the backbone in addition to carbonate groups.Thus, for example, polycarbonate copolymers of alkylene oxide monomersand the previously described alkylene diols can be used. Alkylene oxidemonomers include, for example, ethylene oxide, tetrahydrofuran, and thelike. These copolymers produce cured coatings that exhibit a lowermodulus and also inhibit crystallinity of the liquid coating compositioncompared to polycarbonate diol homopolymers. Admixtures of thepolycarbonate diols and polycarbonate copolymers can also be utilized.

Polycarbonate diols include, for example, Duracarb 122 (PPG Industries)and Permanol KM10-1733 (Permuthane, Inc., Massachusetts). Duracarb 122is produced by the alcoholysis of diethylcarbonate with hexane diol.

Examples of polyester diols include the reaction products of saturatedpolycarboxylic acids, or their anhydrides, and diols. Saturatedpolycarboxylic acids and anhydrides include, for example, phthalic acid,isophthalic acid, terephthalic acid, trimellitic acid,tetrahydrophthalic acid, hexahydrophthalic acid, tetrachlorophthalicacid, adipic acid, azelaic acid, sebacic acid, succinic acid, glutaricacid, malonic acid, pimelic acid, suberic acid, 2,2-dimethylsuccinicacid, 3,3-dimethylglutaric acid, 2,2-dimethylglutaric acid, the like,anhydrides thereof and mixtures thereof. Diols include, for example,1,4-butanediol, 1,8-octane diol, diethylene glycol, 1,6-hexane diol,dimethylol cyclohexane, and the like. Included in this classificationare the polycaprolactones, commercially available from Union Carbideunder the trade designation Tone Polylol series of products, forexample, Tone 0200, 0221, 0301, 0310, 2201, and 2221. Tone Polyol 0301and 0310 are trifunctional.

Any organic polyisocyanate (ii), alone or in admixture, can be used asthe polyisocyanate. Thereby, a product is obtained which is end-cappedwith the reaction product from the isocyanate/ethylenically unsaturatedmonomer reaction on at least one end of the molecule. "End-capped" meansthat a functional group caps one of the two ends of the oligomer diol.

The isocyanate/hydroxy functional monomer reaction product attaches tothe oligomer backbone (i) diol via a urethane linkage. The urethanereactions can take place in the presence of a catalyst. Catalysts forthe urethane reaction include, for example, diazabicyclooctane crystalsand the like.

Preferably the polyisocyanate (ii) is a diisocyanate. Examples ofdiisocyanates (ii) include isophorone diisocyanate (IPDI), toluenediisocyanate (TDI), diphenylmethylene diisocyanate, hexamethylenediisocyanate, cyclohexylene diisocyanate, methylene dicyclohexanediisocyanate, 2,2,4-trimethyl hexamethylene diisocyanate, m-phenylenediisocyanate, 4-chloro-1,3-phenylene diisocyanate, 4,4'-biphenylenediisocyanate, 1,5-naphthylene diisocyanate, 1,4-tetramethylenediisocyanate, 1,6-hexamethylene diisocyanate, 1,10-decamethylenediisocyanate, 1,4-cyclohexylene diisocyanate, and polyalkyloxide andpolyester glycol diisocyanates such as polytetramethylene ether glycolterminated with TDI and polyethylene adipate terminated with TDI,respectively. Preferably, the isocyanates are TDI and IPDI.

Generally the compound providing a reactive terminus (iii) contains afunctional group which can polymerize under the influence of actinicradiation, and the compound contains a functional group which can reactwith the diisocyanate. Hydroxy functional ethylenically unsaturatedmonomers are preferred. More preferably, the hydroxy functionalethylenically unsaturated monomer contains acrylate, (meth)acrylate,vinyl ether, maleate or fumarate functionality.

In the reaction between hydroxy group of (i) and isocyanate groups of(ii), it is preferred to employ a stoichiometric balance between hydroxyand isocyanate functionality and to maintain the reaction temperature ofat least 25° C. The hydroxy functionality should be substantiallyconsumed. The mole ratio of the isocyanate to the hydroxy functionalethylenically unsaturated monomer is about 3:1 to 1.2:1, preferablyabout 2:1 to 1.5:1. The hydroxy functional ethylenically unsaturatedmonomer attaches to the isocyanate via an urethane linkage. Monomershaving (meth)acrylate functional groups include, for example, hydroxyfunctional acrylates such as 2-hydroxyethyl acrylate, 2-hydroxypropylacrylate, and the like. Monomers having vinyl ether functional groupsinclude, for example, 4-hydroxybutyl vinyl ether, and triethylene glycolmonovinyl ether. Monomers having maleate functional groups include, forexample, maleic acid and hydroxy functional maleates.

Component B. is a radiation-curable oligomer according to the followingformula:

    R.sup.1 -L.sup.1 -C.sup.1 -L.sup.2 -R.sup.2                (1)

where:

R¹ and R², independently, each represent a radiation-curable functionalgroup;

L¹ and L², independently, each represent an alkyloxy chain having fromabout 2 to about 40 carbon atoms, wherein L¹ and L² are linked to C¹through an oxygen atom;

C¹ comprises a hydrocarbon having from about 5 to about 40 carbon atomsand containing at least one cyclic group.

Radiation-curable functional groups are well known and within the skillof the art. Based on the disclosure provided herein, one skilled in theart will know what radiation-curable functional groups to use as R¹ andR², to provide the desired curing properties.

Commonly, the radiation-curable functionality used is ethylenicunsaturation, which can be polymerized through radical polymerization orcationic polymerization. Specific examples of suitable ethylenicunsaturation are groups containing acrylate, methacrylate, styrene,vinylether, vinyl ester, N-substituted acrylamide, N-vinyl amide,maleate esters, and fumarate esters. Preferably, the ethylenicunsaturation is provided by a group containing acrylate, methacrylate,or styrene functionality.

Another type of functionality generally used is provided by, forexample, epoxy groups, or thiol-ene or amine-ene systems. Epoxy groupsin can be polymerized through cationic polymerization, whereas thethiol-ene and amine-ene systems are usually polymerized through radicalpolymerization. The epoxy groups can be, for example, homopolymerized.In the thiol-ene and amine-ene systems, for example, polymerization canoccur between a group containing allylic unsaturation and a groupcontaining a tertiary amine or thiol.

The groups L¹ and L² are each alkyloxy chains having from about 2 toabout 40 carbon atoms, preferably about 2 to about 20 carbon atoms, andmost preferably about 2 to about 10 carbon atoms. The groups L¹ and L²each comprise about 1 to about 12 alkylether groups, and preferably,from about 1 to about 6 alkylether groups. Examples of suitablealkylether groups include ethylether, propylether and butylether. Thealkylether groups can also contain cyclic groups. Preferably, thealkylether group is made from an epoxy containing alkane, such aepoxyethane, epoxypropane, and epoxybutane.

The groups L¹ and L² connect to C¹ through an oxygen atom. The oxygenconnecting the group L¹ to the group C¹ is considered part of the groupL¹ and the oxygen connecting the group L² to the group C¹ is consideredpart of the group L².

The group C¹ comprises about 5 to about 40 carbon atoms and contains atleast one cyclic group. Preferably, the group C¹ comprises about 5 toabout 20 carbon atoms.

The cyclic groups can be saturated or fully or partially unsaturatedcyclic alkylene groups. Examples of suitable saturated cyclic alkylenegroups include, but are not limited to, cyclopentane, cyclohexane,cycloheptane, and cyclooctane. Cylcopentane and cyclohexane arepreferred. The cyclic alkylene groups can also be partially unsaturatedsuch as cyclobutene, cyclopentene, cyclohexene, cycloheptene, andcyclooctene. Cyclopentene and cyclohexene are preferred. Furtherexamples of suitable cyclic alkylene groups include arylenes, such asbenzene and naphthalene. Preferably, the cyclic group is benzene.

The cyclic groups can be substituted with hydrocarbon groups, such asmethyl, ethyl, propyl, and butyl groups.

Preferably, the group C¹ comprises at least two cyclic groups which areeither directly connected or connected via one or more hydrocarbongroups. Examples of such preferred groups C¹ are represented by thefollowing formulae (2) or (3):

    X.sup.1 -X.sup.2                                           (2)

    X.sup.1 -Y.sup.1 -X.sup.2                                  (3)

Where:

X¹ and X² are each cyclic alkylene groups as described herein; and

Y¹ is a hydrocarbon having from about 1 to about 15 carbon atoms,preferably about 1 to about 10 carbon atoms.

Preferably X¹ and X² are arylenes.

The Y¹ group can be saturated or unsaturated, and branched or linear.Examples of suitable saturated Y¹ groups include, methyl, ethyl, propyl,and butyl.

Specific examples of suitable groups C¹ are derived from bisphenol A,saturated bisphenol A, bisphenol F, saturated bisphenol F,tricyclodecane dimethanol or cyclohexane dimethanol.

An example of a suitable Component B. is an alkoxylated bisphenoldi(meth)acrylate. The alkoxylated bisphenol di(meth)acrylate can be anyalkoxylated bisphenol di(meth)acrylate and can be prepared in any knownmanner. Preferably, Component B. is an alkoxylatedbisphenol-A-diacrylate. Preferably the alkoxylatedbisphenol-A-di(meth)acrylate is an ethoxylated or propoxylatedbisphenol-A-diacrylate. An example of a particularly suitablealkoxylated bisphenol-A-diacrylate is ethoxylatedbisphenol-A-diacrylate, commercially available as SR 349A Monomer,supplied by Sartomer.

The alkoxylated bisphenol-A-di(meth)acrylate B. is preferably present inan amount of about 10 to about 80% by weight, more preferably about 40to about 80% by weight, and most preferably about 50 to about 70% byweight.

The composition according to the invention may comprise a reactivediluent as Component C. The reactive diluent can be used to adjust theviscosity of the coating composition. Thus, the reactive diluent can bea low viscosity monomer containing at least one functional group capableof polymerization when exposed to actinic radiation.

The reactive diluent is preferably added in such an amount that theviscosity of the coating composition is in the range of about 1,000 toabout 10,000 mPas. Suitable amounts of the reactive diluent have beenfound to be about 1 to about 20% by weight, and more preferably about 5to about 15% by weight.

The reactive diluent preferably has a molecular weight of not more thanabout 550 or a viscosity at room temperature of not more than about 300mPa.s (measured as 100% diluent).

The radiation-curable functional group present on the reactive diluentmay be of the same nature as that used in the radiation-curable oligomerA. or Component B. Preferably, the radiation-curable functional grouppresent in the reactive diluent is capable of copolymerizing with theradiation-curable functional group present on the radiation-curableoligomer A or Component B.

Preferably, reactive diluent C. comprises a monomer or monomers havingan acrylate or vinyl ether functionality and an C₄ -C₂₀ alkyl orpolyether moiety. Examples of such reactive diluents are

hexylacrylate,

2-ethylhexylacrylate,

isobornylacrylate,

decylacrylate,

laurylacrylate,

stearylacrylate,

ethoxyethoxy-ethylacrylate,

laurylvinylether,

2-ethylhexylvinyl ether,

N-vinyl formamide,

isodecyl acrylate,

isooctyl acrylate,

vinyl-caprolactam,

N-vinylpyrrolidone and the like.

This type of reactive diluent preferably is present in an amount betweenabout 1 and about 35 wt. %.

Another preferred type of reactive diluent is a compound comprising anaromatic group. Examples of diluents having an aromatic group include:

ethyleneglycolphenyletheracrylate,

polyethyleneglycolphenyletheracrylate,

polypropyleneglycolphenyletheracrylate, and

alkyl-substituted phenyl derivatives of the above monomers, such as

polyethyleneglycolnonylphenyletheracrylate.

This type of reactive diluent preferably is present in an amount betweenabout 1 and about 35 wt. %.

Furthermore, reactive diluent C. preferably contains two groups capableof polymerization using actinic radiation. A diluent having three ormore of such reactive groups can be present as well. Examples of suchmonomers include:

C₂ -C₁₈ hydrocarbondioldiacrylates,

C₄ -C₁₈ hydrocarbondivinylethers,

C₃ -C₁₈ hydrocarbontrioltriacrylates,

the polyether analogues thereof, and the like, such as

1,6-hexanedioldiacrylate,

trimethylolpropanetriacrylate,

hexanedioldivinylether,

triethyleneglycoldiacrylate,

pentaeritritoltriacrylate, and

tripropyleneglycol diacrylate.

Preferably the reactive diluent is an alkoxylated alkyl phenol(meth)acrylate, most preferably an ethoxylated nonyl phenol(meth)acrylate.

If the radiation-curable functional group of the radiation-curableoligomer A. or Component B. is an epoxy group, for example, one or moreof the following compounds can be used as the reactive diluent:

epoxy-cyclohexane,

phenylepoxyethane,

1,2-epoxy-4-vinylcyclohexane,

glycidylacrylate,

1,2-epoxy-4-epoxyethyl-cyclohexane,

the diglycidylether of polyethylene-glycol, the diglycidylether ofbisphenol-A, and the like.

If the radiation-curable functional group of the radiation-curableoligomer A. or Component B. has an amine-ene or thiol-ene system,examples of reactive diluents having allylic unsaturation that can beused include:

diallylphthalate,

triallyltri-mellitate,

triallylcyanurate,

triallylisocyanurate, and

diallylisophthalate.

For amine-ene systems, amine functional diluents that can be usedinclude, for example:

the adduct of trimethylolpropane, isophorondiisocyanate anddi(m)ethylethanolamine, the adduct of hexanediol, isophorondiisocyanateand dipropylethanolamine, and the adduct of trimethylol propane,trimethylhexamethylenediisocyanate and di(m)ethylethanolamine.

Preferably, the oligomer A., the oligomer B. and the reactive diluent C.(if present) each contain an acrylate group as a radiation-curablegroup. More preferably, R¹ and R² are both acrylate groups, theethylenic unsaturation on said oligomer A. is provided by acrylategroups, and the reactive diluent C. (if present) contains an acrylategroup.

The photoinitiator, Component D., is useful when conducting anultraviolet radiation-cure. In other embodiments, for example, whenusing an electron beam cure of a free radical system, the photoinitiatorD. can be omitted. In cationally cured systems, however, aphotoinitiator D. is useful even when performing an electron beam cure.

The photoinitiator D., when used in an effective amount to promoteradiation cure, preferably provides reasonable cure speed withoutcausing premature gelling of the composition. The cure speed desiredwill depend on the application of the coating and a skilled artisan willeasily be able to adjust the amount and type of photoinitiator to obtainthe desired cure speed. The type of photoinitiator which is used will bedependent on whether a free radical-type system or a cationic curetype-system is used.

Examples of free radical-type photoinitiators include, but are notlimited to, the following:

hydroxycyclohexylphenylketone;

hydroxymethylphenylpropanone;

dimethoxyphenylacetophenone;

2-methyl-1-[4-(methyl thio)-phenyl]-2-morpholino-propanone 1;

1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one;

1-(4-dodecyl-phenyl)-2-hydroxy-2-methylpropan-1-one;

4-(2-hydroxyethoxy)phenyl-2(2-hydroxy-2-propyl)-ketone;

diethoxyphenyl acetophenone;

2,4, 6 trimethylbenzoyl diphenylphosphone;

a mixture of (2,6-dimethoxy benzoyl)-2,4,4 trimethylpentylphosphineoxideand 2-hydroxy-2-methyl-1-phenyl-propan-1-one; and

mixtures of these.

Examples of cationic cure-type photoinitiators include, but are notlimited to, onium salts such as iodonium, sulfonium, arsonium, azonium,bromonium, or selenonium. The onium salts are preferably chemicallymodified to render them more hydrophobic, for example, by incorporatingsaturated hydrocarbon moieties such as alkyl or alkoxy substituents offrom about 4 to about 18 carbon atoms. Preferred cationic cureinitiators include:

(4-octyloxyphenyl)phenyl iodonium hexafluoro antimonate;

(4-octyloxyphenyl)diphenyl sulfonium hexafluoro antimonate;

(4-decyloxyphenyl)phenyl iodonium hexafluoro antimonate; and

(4-octadecyloxyphenyl)phenyl iodonium hexafluoro antimonate.

When a pigment E. is present in the composition according to theinvention, it is preferred to use as component D. an acyl phosphineoxide photoinitiator, more specifically a benzoyl diaryl phosphine oxidephotoinitiator. Such a photoinitiator provides a high cure speed even inthe presence of relatively high amounts of pigment. Published PCTapplication WO 90/13579 discloses coating compositions containingpigments, and is incorporated herein by reference. Examples of suitablebenzoyl diaryl phosphine oxide photoinitiators include:

2,4,6-trimethylbenzoyldiphenyl-phosphine oxide (Lucirin TPO by BASF),and

bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl-phosphine oxide(Irgacine 1700 by Ciba Geigy).

For an optimum cure speed in the presence of pigment, it is advantageousto combine an acyl phosphine oxide photoinitiator with one or more otherphotoinitiators, such as hydroxycyclohexylphenylketone.

The photoinitiator is preferably present in an amount of about 1 toabout 20% by weight, more preferably in an amount of about 1 to about10% by weight, and most preferably, about 1 to about 5% by weight.

The pigment E. can be any pigment suitable for use in pigmented coloredoptical fiber coatings. Preferably, the pigment E. is in the form ofsmall particles and is capable of withstanding UV-radiation. Examples ofsuitable pigments include:

titanium dioxide white (Dupont R-960),

carbon black (Degussa Special 4A or Columbian Raven 420),

lamp black (General carbon LB#6),

phthalo blue G (Sun 249-1282),

phthalo blue R (Cookson BT698D),

phthalo green B (Sun 264-0238),

phthalo green Y (Mobay G5420),

light chrome yellow (Cookson Y934D),

diarylide yellow (Sun 274-3954),

organic yellow (Hoechst H4G),

medium chrome yellow (Cookson Y969D),

yellow oxide (Pfizer YL02288D),

lead free-yellow (BASF Paliotol 1770),

raw umber (Hoover 195),

burnt umber (Lansco 3240X),

lead free orange (Hoechst RL70),

red oxide (Pfizer R2998D),

moly orange (Cookson YL988D),

arylide red (Hoechst F5RKA),

quinacridone red (Ciba RT759D), and

quinacridone violet (Ciba RT887D).

Preferably, the pigment has a mean particle size of not more than about1 μm. The particle size of the commercial pigments can be lowered bymilling if necessary. The pigment is preferably present in an amount ofabout 1 to about 10% by weight, and more preferably in an amount ofabout 3 to about 8% by weight.

Other components that can be present in the composition include, but arenot limited to, light sensitive and light absorbing components,catalysts, initiators, lubricants, wetting agents, organofunctionalsilanes, antioxidants, and stabilizers, which do not interfere with thedesired resistance to moisture. These additives may be added to thecompositions according to the invention in an amount that is usual forthe additive when used in optical fiber coatings.

The examples of polymeric coating compositions set forth above areintended only to be illustrative of the coating compositions that may beemployed in the present invention. The compositions according to theinvention can be applied on an optical fiber using conventional coatingtechnology.

In producing a coated optical fiber, a liquid coating composition isapplied to a substrate and subsequently cured. Typically, the cure isaffected using ultraviolet or visible radiation. However, other methodsof curing can be used. For example, thermal curing, usually in thepresence of an initiator, can be used. Alternatively, the coating can becured by electron beam irradiation where no catalyst is required. Morethan one coating can be applied. Typically, a first coating is appliedand cured followed by a second coating and so on until the desirednumber of coatings have been applied. Alternatively, the layers can beapplied on top of each other as liquids, typically referred to as awet-on-wet process, with one final curing step at the end.

For example, on a bare glass fiber having a diameter of about 125 μm, aUV-curable inner primary coating can be provided, such that the fiberwith inner primary coating has a diameter of about 180 μm. Then, thecoating composition according to the invention can be applied in athickness of between about 10 and about 150 μm, and preferably betweenabout 20 and about 60 μm, and then cured.

Although the coating composition is suitable as an outer primarycoating, it is also possible to use the compositions described herein asa single coating on the glass optical fiber. Single coatings can be madewhich have a sufficiently low modulus that it they minimize themicrobending problems at low temperatures and which are hard and toughenough to protect the optical glass fiber.

The invention will be further explained by the following non-limitingexamples.

EXAMPLE I

A coating composition was prepared by mixing the following components:

    ______________________________________                                        Component:            Percent                                                 ______________________________________                                        Polyether urethane acrylate                                                                         28.7                                                    Ethoxylated bisphenol-A-diacrylate                                                                  56.0                                                    Ethoxylated nonylphenolacrylate                                                                     7.2                                                     [Photomer 4003 by Henkel]                                                     2,4,6-trimethylbenzoyldiphenyl-                                                                     0.9                                                     phosphine oxide                                                               [Lucirin TPO by BASF]                                                         Hydroxycyclohexylphenylketone                                                                       1.8                                                     [Irgacure 184 by Ciba Geigy]                                                  Thiodiethylene-bis -  0.4                                                     (3,5-di-tert-butyl-4-hydroxy)                                                 hydrocinnamate                                                                [Irganox 1035 by Ciba Geigy]                                                  Bis(1,2,2,6,6,pentamethyl-4-piperidinal)                                                            0.4                                                     sebacate                                                                      [Tinuvin 292 by Ciba Geigy]                                                   Titanium dioxide, rutile                                                                            5.0                                                     ______________________________________                                    

The polyether urethane acrylate was prepared as follows:

Toluene Diisocyanate (119.15 g; 1.3664 equivalents), commerciallyobtained as Mondur TD-80 Grade A from Mobay, Inc. of Pittsburgh, Pa. wascombined with BHT, a preservative (0.53 g). The mixture was charged intoa one liter, 4-necked round bottom flask.

The flask was equipped with a stirrer, a dry air sparge, a refluxcondenser, a thermometer and a heating mantle on an automatic jackcontrolled by a thermostat. The mixture was held at 26° C. (78.8° F.)and 2-hydroxyethyl acrylate (HEA) 84.94 grams; 0.7315 equivalents) wasadded to the flask containing the mixture over a two (2) hour and twenty(20) minute period.

The mixture was maintained at 26.6° C. (78.8° F. for about three (3)hours after which it was heated to 50° C. 122° F.). PTGL 1000 (277.72 g;0.6073 g equivalents, made by Hodogaya Chemical, Japan, was added all atonce to the mixture. PTGL 1000 is a copolymer of 3-methyltetrahydrofuranand tetrahydrofuran, both of which have undergone a ring openingpolymerization. The PTGL 1000 is the polymerization product of about 20percent by weight 3-methyltetrahydrofuran and about 80 percent by weightof tetrahydrofuran.

The resulting mixture was allowed to mix for five minutes.Diazabicyclooctane crystals (0.25 g), (DABCO crystals), from AirProducts in Allentown, Pa., were then added to the mixture. Theexothermic reaction was permitted to heat the mixture to 83° C. (181.4°F.). The contents of the flask were then held at 70° C. (158° F.) untilthe percent of free isocyanate in the oligomer was negligible (<0.1percent).

The structure of the resulting oligomer is represented schematically asHEA-(-TDI-PTGL 1000)₀.8 -TDI-HEA.

EXAMPLE II

A coating composition was prepared in the same manner as Example 1. Thesame polyether urethane acrylate as in Example I was used in thefollowing composition:

    ______________________________________                                        Component:           Percent                                                  ______________________________________                                        Polyether urethane acrylate                                                                        32.5                                                     Ethoxylated bisphenol-A-diacrylate                                                                 56.0                                                     Ethoxylated nonylphenolacrylate                                                                    8.0                                                      [Photomer 4003 by Henkel]                                                     2,4,6-trimethylbenzoyldiphenyl-                                                                    1.0                                                      phosphine oxide                                                               [Lucirin TPO by BASF]                                                         Hydroxycyclohexylphenylketone                                                                      2.0                                                      [Irgacure 184 by Ciba Geigy]                                                  Thiodiethylene-bis-  0.5                                                      (3,5-di-tert-butyl-4-hydroxy)                                                 hydrocinnamate                                                                [Irganox 1035 by Ciba Geigy]                                                  ______________________________________                                    

Comparative Example A

A coating composition was prepared by mixing the following components:

    ______________________________________                                        Component:             Percent                                                ______________________________________                                        Polyether urethane acrylate                                                                          49.1                                                   Epoxy acrylate         8.6                                                    Trimethylol propane triacrylate                                                                      7.1                                                    N-vinyl pyrrolidone    3.9                                                    N-vinyl caprolactam    7.9                                                    Phenothiazine (stabilizer)                                                                            0.01                                                  2,4,6-trimethylbenzoyldiphenyl phosphine                                                             2.4                                                    oxide                                                                         Silicone oil [DC 193 from DOW Corning]                                                               0.2                                                    2-hydroxyethylacrylate 0.8                                                    Titanium dioxide, rutile                                                                             20.0                                                   ______________________________________                                    

The polyether urethane acrylate was the reaction product of astoichiometric proportion of 2-hydroxyethyl acrylate with anisocyanate-terminated oligomer, which is the urethane reaction productof polyoxytetramethylene glycol of a molecular weight 650 with toluenediisocyanate. The product had a NCO-content of 7.5% by weight. Theisocyanate-terminated product used had a viscosity at 30° C. of 8000centipoises.

The epoxy acrylate was the diacrylate of Epon 828 (Shell) which is adiglycidyl ether of bisphenol A having a molecular weight of 390.

The above mixture was sandmilled to a particle size finer thanrepresented by a 7.5 North Standard grind gauge rating and checked bylight microscopy to make sure that no particles having a size greaterthan 1 micron (1 micrometer) were present.

Comparative Example B

A coating composition was prepared using the following:

    ______________________________________                                        Component:             Percent                                                ______________________________________                                        Polycaprolactone urethane acrylate                                                                   41.4                                                   Phenoxyethyl acrylate  45.1                                                   Trimethylol propane triacrylate                                                                      5.0                                                    2,4,6-trimethylbenzoyldiphenyl phosphine                                                             3.0                                                    oxide                                                                         Silicone oil [DC 203 from DOW Corning]                                                                0.01                                                  Titanium dioxide, rutile                                                                             5.0                                                    Triethanol amine       0.5                                                    ______________________________________                                    

The above mixture was sandmilled to a particle size finer thanrepresented by a North Standard grind gauge rating and checked by lightmicroscopy to make sure that no particles having a size greater than 1micron was present.

Comparative Example C

The white colored secondary coating composition from Neorad F480 (ICI)was used.

The coating compositions prepared in Examples I and II, and Comparativeexamples A-C, were applied as a 3 mil film on a glass plate and cured bypassing beneath a single fusion "D" lamp at 1.0 J/cm2 in a nitrogenatmosphere. The properties of the cured films were measured according tothe test procedures provided below. The results are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        Properties of coating compositions                                                                   Comp.    Comp. Comp.                                            Exp. I                                                                              Exp. II Exp. A   Exp. B                                                                              Exp. C                                  ______________________________________                                        Film       150     75      75     150   150                                   thickness (μ)                                                              clarity    opaque  clear   opaque opaque                                                                              opaque                                color      white   clear   white  white white                                 viscosity  5390    6200    24,250 2550  12,850                                (mPa · s)                                                            95% cure   1.4     0.2     ˜6                                                                             0.3   0.7                                   (J/cm.sup.2)                                                                  tensile (MPa)                                                                            18      24      --     20    36                                    elongation 7       18      --     27    22                                    (%)                                                                           modulus (MPa)                                                                            500     560     --     670   1100                                  T.sub.E' = 1000 (° C.)                                                            17      20      24     31    46                                    T.sub.E' = 100 (° C.)                                                             47      52      77     43    76                                    tan delta max                                                                            49      53      78     45    >8                                    (° C.)                                                                 E.sub.o (MPa)                                                                            22      26      33     11    13                                    after aging:                                                                  T.sub.E' = 1000 (° C.)                                                            22      22      19     38    61                                    T.sub.E' = 100 (° C.)                                                             51      53      75     49    89                                    tan delta max                                                                            52      56      74     51    94                                    (° C.)                                                                 E.sub.o (MPa),                                                                           23      24      25     7     9                                     (increase, %)                                                                            (+5%)   (-8%)   (-24%) (-36%)                                                                              (-31%)                                Color      white   clear   yellowed                                                                             white yellowed                              Peak water 1.1     1.2     3.2    2.1   6.6                                   absorption                                                                    (%)                                                                           Water soak 1.4     0.8     1.7    0.6   3.8                                   Extraction                                                                    (%)                                                                           Total water                                                                              2.5     2.0     4.9    2.7   10.4                                  sensitivity                                                                   (%)                                                                           ______________________________________                                    

From Table 1, it is clear that the coating compositions of Examples Iand II, according to the invention, produced cured coatings having abetter peak water absorption than the coatings produced from the coatingcompositions of Comparative Examples A, B and C. The coatings producedusing the coating compositions according to the invention also exhibitedan enhanced stability in the aging test. In particular, the modulusincreased only 5% in Example I and decreased only 8% in Example II. Incontrast, the comparative coatings decreased from 24% to 36%. Moreover,the color of the coatings of Examples I and II is unchanged after aging.Furthermore, the coatings of Examples I and II exhibited a goodresistance against attack from hydrocarbon gel.

Test Procedures

The water soak extraction and absorption were measured using thefollowing procedure. A drawdown of each material to be tested was madeat a film thickness as indicated in Table 1 on a glass plate and cured.The cured film was cut to form three sample specimens, approximately 3cm×3 cm on the glass plate. The glass plate containing the three samplespecimens was heated at 80° C. for one hour and then placed in adesiccator for 15 minutes. The relative humidity and temperature of thedesiccator were measured.

125 ml (4 oz.) of deionized or distilled water was poured into three 125ml (4 oz.) glass jars, maintained at a temperature of 23±2° C. Each ofthe sample specimens were removed from the glass plate and weighed on ananalytical balance using corrugated Teflon paper to prevent sticking.Each sample specimen was then placed into one the jars of water.

The sample specimens were soaked in the water for 30 minutes and thenremoved from the glass jars. The water remaining on the surface of thesample specimens was removed by blotting them with lint free wipingtissue.

The samples were reweighed as above and placed back into theirrespective jars.

The above procedure was repeated at 1, 2, 3, and 24 hours, and at 7 and14 days.

At 21 days, the sample specimens were removed from the glass jars andreweighed as above. The sample specimens were placed onto a glass plateand heated at 80° C. for one hour, and then placed in a desiccator for15 minutes. The relative humidity and temperature of the desiccator weremeasured. The sample specimens were reweighed as before.

The percent weight change at each time interval for each sample specimenwas determined. The values for the three sample specimens at each timeinterval were averaged. The water absorption reported is the largest,positive average percent weight change.

The water extraction for each sample specimen was determined by dividingthe difference of the initial and 21-day dried weights by the initialdried weight and multiplying by 100. The reported value is the averageof the three sample specimen values.

The total water sensitivity is the sum of the absolute values of thewater absorption and the water extraction.

The elastic modulus (E'), the viscous module (E'), and the tan delta max(E"/E') of the examples were measured using a Rheometrics SolidsAnalyzer (RSA-11), equipped with: 1) A personal computer having MS-DOS5.0 or later operating system and having Rhios® software (Version 4.2.2or later) loaded; 2) A liquid nitrogen controller system forlow-temperature operation.

The test samples were prepared by casting a film of the material, havinga thickness in the range of 0.02 mm to 0.4 mm, on a glass plate. Thesample film was cured using a UV processor. A specimen approximately 35mm (1.4 inches) long was cut from a defect-free region of the curedfilm. For soft films, which tend to have sticky surfaces, acotton-tipped applicator was used to coat the cut specimen with talcpowder.

The film thickness of the specimen was measured at five or morelocations along the length. The average film thickness was calculated to±0.001 mm. The thickness cannot vary by more than 0.01 mm over thislength. Another specimen was taken if this condition was not met. Thewidth of the specimen was measured at two or more locations and theaverage value calculated to ±0.1 mm.

The geometry of the sample was entered into the instrument. The lengthfield was set at a value of 23.2 mm and the measured values of width andthickness of the sample specimen were entered into the appropriatefields.

Before conducting the temperature sweep, moisture was removed from thetest samples by subjecting the test samples to a temperature of 80° C.in a nitrogen atmosphere for 5 minutes. The temperature sweep usedincluded cooling the test samples to about -60° C. to about -70° C. andincreasing the temperature at about 1° /minute until the temperaturereached about 60° C. to about 70° C. The test frequency used was 1.0radian/second.

The tensile strength of cured samples was tested using a universaltesting instrument, Instron Model 4201 equipped with a personal computerand software "Series IX Materials Testing System." The cells were loadedat a 2 and 20 pound capacity. The ASTM D638M was followed, with thefollowing modifications.

A drawdown of each material to be tested was made on a glass plate andcured using a UV processor. The cured film was conditioned at 23±2° C.and 50±5% relative humidity for a minimum of sixteen hours prior totesting.

A minimum of eight test specimens, having a width of 0.5±0.002 inchesand a length of 5 inches, were cut from the cured film. If the curedfilm was tacky to the touch, a small amount of talc was applied to thefilm surface using a cotton tipped applicator.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one of ordinaryskill in the art that various changes and modifications can be madetherein without departing from the spirit and scope thereof.

What is claimed is:
 1. A coated glass optical fiber coated with aradiation cured outer primary coating obtained from a compositioncomprising as premixture components, the combination of:about 20 toabout 40% by weight of a polyether urethane first oligomer comprisingethylenically unsaturated groups; from about 5 to about 20% by weight ofa reactive diluent; from 0 to about 40% by weight of a photoinitiator;from 0 to about 10% by weight of a pigment; and about 40 to about 80% byweight of a radiation-curable second oligomer represented by thefollowing formula:

    R.sup.1 -L.sup.1 -C.sup.1 -L.sup.2 -R.sup.2                ( 1)

where: R¹ and R², independently, each represent a radiation-curableethylenically unsaturated functional group; L¹ and L², independently,each represent an alkyloxy chain having from about 2 to about 40 carbonatoms, wherein L¹ and L² are linked to C¹ through an oxygen atom; and C¹comprises a hydrocarbon having from about 5 to about 40 carbon atoms andcontaining at least one cyclic group; wherein said composition, afterradiation-cure, has a peak water absorption of no more than 1.5%.
 2. Thecoated glass optical fiber according to claim 1, wherein said coatingcomposition comprises:about 1 to about 20% by weight of saidphotoinitiator.
 3. The coated glass optical fiber according to claim 1,wherein said coating composition comprises about 1 to about 10% byweight pigment.
 4. The coated glass optical fiber according to claim 1,wherein said groups R¹ and R², independently, contain aradiation-curable functional group selected from the group consisting ofacrylate, methacrylate, styrene, vinylether, acrylamide, maleate andfumarate.
 5. The coated glass optical fiber according to claim 1 whereinsaid groups R¹ and R² are acrylate, and said polyether urethane oligomercontains at least one acrylate group.
 6. The coated glass optical fiberaccording to claim 1, wherein said groups L¹ and L², independently, arealkyloxy groups containing from about 1 to about 12 alkylether groups.7. The coated glass optical fiber according to claim 6, wherein saidalkylether groups are selected from the group consisting of ethylether,propylether, and butylether.
 8. The coated glass optical fiber accordingto claim 1, wherein group C¹ is represented by the following formulae(2) or (3):

    X.sup.1 -X.sup.2                                           ( 2)

    X.sup.1 -Y.sup.1 -X.sup.2                                  ( 3)

Where: X¹ and X² are each cyclic alkylene groups; and Y¹ is ahydrocarbon having from about 1 to about 15 carbon atoms.
 9. The coatedglass optical fiber according to claim 1, wherein the group C¹ isderived from a member of the group consisting of bisphenol A, saturatedbisphenol A, bisphenol F, saturated bisphenol F, tricyclodecanedimethanol and cyclohexane dimethanol.
 10. The coated glass opticalfiber according to claim 1, wherein said radiation-curable oligomeraccording to formula (1) is an ethoxylated or propoxylatedbisphenol-A-diacrylate.
 11. The coated glass optical fiber according toclaim 1, wherein said polyether urethane oligomer has a calculatedaverage molecular weight between about 500 and about
 2000. 12. Thecoated glass optical fiber according to claim 1, wherein saidcomposition, after radiation-cure, has:an elongation at break of atleast about 5%; a room temperature tensile modulus of at least about 400MPa; and a glass transition temperature, tan delta max., of at leastabout 40° C.
 13. The coated glass optical fiber according to claim 1,wherein said second radiation-curable oligomer is an alkoxylatedbisphenol di (meth)acrylate.
 14. A coated glass optical fiber coatedwith a radiation cured coating obtained from a composition comprising aspremixture components:about 10 to about 80% by weight of anethylenically unsaturated polyether urethane first oligomer having amolecular weight of at least about 500 daltons; about 10 to about 80% byweight of a radiation-curable second oligomer according to the followingformula:

    R.sup.1 -L.sup.1 -C.sup.1 -L.sup.2 -R.sup.2                ( 1)

wherein R¹ and R², independently, each represent an ethylenicallyunsaturated radiation-curable functional group; L¹ and L²,independently, each represent an alkyloxy chain having from about 2 toabout 40 carbon atoms, wherein L¹ and L² are linked to C¹ through anoxygen atom; and C¹ comprises a hydrocarbon having from about 5 to about40 carbon atoms and containing at least one cyclic group;from 0 to about40% by weight of a reactive diluent; from 0 to about 40% by weight of aphotoinitiator; and from 0 to about 10% by weight of a pigment, whereinsaid composition, after radiation-cure, has:an elongation at break of atleast about 5%; a peak water absorption of no more than 1.5%; a roomtemperature tensile modulus of 50-560 MPa; a glass transitiontemperature, tan delta max., of at least about 40° C.; hydrolyticstability; and resistance to attack from hydrocarbon gel cable fillingmaterial.
 15. In a formulation for a coated optical glass fiber, acoating composition containing at least 20 wt % of one first radiationcurable polyether urethane oligomer, the improvementcomprising:incorporating a second radiation-curable oligomer accordingto the following formula:

    R.sup.1 -L.sup.1 -C.sup.1 -L.sup.2 -R.sup.2                ( 1)

where: R¹ and R², independently, each represent an ethylenicallyunsaturated radiation-curable functional group; L¹ and L²,independently, each represent an alkyloxy chain having from about 2 toabout 40 carbon atoms, wherein L¹ and L² are linked to C¹ through anoxygen atom; C¹ comprises a hydrocarbon having from about 5 to about 40carbon atoms and containing at least one cyclic group, wherein saidcoating composition when radiation cured exhibits:a peak waterabsorption of no more than 1.5%.
 16. The formulation according to claim15, wherein said coating composition when radiation cured exhibits:anelongation at break of at least about 5%; a room temperature tensilemodulus of at least about 400 MPa; and a glass transition temperature Tg(tan delta max) of at least about 40° C.
 17. The formulation accordingto claim 15, wherein said groups R¹ and R², independently, contain aradiation-curable functional group selected from the group consisting ofacrylate, methacrylate, styrene, vinylether, acrylamide, maleate andfumerate.
 18. The formulation according to claim 15, wherein said groupsR¹ and R² are acrylate.